Three-port nonreciprocal circuit device, composite electronic component, and communication apparatus

ABSTRACT

A center-electrode assembly ( 13 ) has a configuration in which center electrodes ( 21 ) to ( 23 ) are arranged, in an electrically insulated state, at the upper surface of a circular-plate microwave ferrite ( 20 ). The center electrode ( 21 ) is constituted by a first line conductor ( 21   a ) and a second line conductor ( 21   b ) which are arranged parallel to each other. The hot ends of the first line conductor ( 21   a ) and the second line conductor ( 21   b ) have connection portions ( 27 ) and ( 26 ), respectively, and the cold ends are connected to a ground electrode ( 25 ). The first and second line conductors ( 21   a ) and ( 21   b ) are arranged such that the hot end of the first line conductor ( 21   a ) and the cold end of the second line conductor ( 21   b ) oppose each other and the cold end of the first line conductor ( 21   a ) and the hot end of the second line conductor ( 21   b ) oppose each other to cause electromagnetic coupling.

TECHNICAL FIELD

The present invention relates to a three-port nonreciprocal circuitdevice, such as an isolator, used in a microwave band and also relatesto a composite electronic component and a communication apparatus.

BACKGROUND ART

Conventionally, a balun, hybrid, or power combiner is provided at theoutput side of a balanced output circuit, particularly, a push-pullamplifier (having a pair of amplifiers that operate at a phasedifference of 180°). The balun or the like converts a balanced signalinto a single-ended signal.

In generally, baluns are used in the microwave band and lower (the HFband, VHF band, UHF band, and lower). On the other hand, hybrids orpower combiners are used in the microwave band and higher (the UHF bandand higher). Wideband ferrite cores are often used for the baluns, inwhich case, the available frequency upper limit is the UHF band.Typically, hybrids or power combiners are configured withdistributed-constant circuits. Thus, the sizes do not cause asignificant problem in practice, for the UHF band or higher.

Meanwhile, in a communication apparatus, particularly, in a transmissioncircuit section for QPSK or the like involving amplitude modulationcomponents or in a transmission circuit section that requires highreliability, a transmission signal converted into a single-ended signalis sent through an isolator and then through an antenna switching device(or antenna duplexer) and the resulting signal is sent to an antenna.Unless the signal is sent through the isolator, reflections from theantenna and the antenna switching device return to a balanced outputcircuit (especially, amplifiers), thereby varying load impedance viewedfrom the balanced output circuit. When the load impedance varies, someproblems arise. For example, the waveform distortion of the transmissionsignal becomes severe and the operation of the amplifiers becomesunstable for oscillation.

However, when a balun (or a hybrid or a power combiner) and an isolatorare combined as in the conventional manner, the size and cost of thetransmission circuit section increase, thereby making it impossible tomeet recent demands for miniaturization and cost reduction of mobilecommunication apparatuses. Also, since a transmission signal passesthrough both the balun and the isolator, the insertion loss isincreased. Further, since the transmission circuit section handles alarge amount of power, when the number of connection portions increasesas a result of an increase in the number of components, there areproblems in that unwanted radiation is easily produced and thepossibility of mutual interference in the communication apparatusincreases. In addition, since the operating bandwidths of the balun andthe isolator reduce the operating bandwidth of the transmission circuitsection, there is a problem in that the available frequency band isreduced.

Accordingly, as described in Japanese Unexamined Patent ApplicationPublication No. 2002-299915, the present inventor proposed anonreciprocal circuit device that can be connected to a balanced outputcircuit without a balun, hybrid, or the like interposed therebetween andalso proposed a communication apparatus. In the nonreciprocal circuitdevice, two opposite ends of a center electrode for one port areconfigured as hot ends, and balanced input and unbalanced output areemployed. The nonreciprocal circuit device can be used to combineoutputs from a push-pull amplifier. However, with the circuit device, inthe case of a low operating point (an operating point at which theamount of bias current, i.e., idling current, is small), reverse-phaseexcitation current does not effectively flow through areverse-phase-side input terminal. Thus, a problem has been found inthat the ferrite excitation efficiency is insufficient.

DISCLOSURE OF INVENTION

Accordingly, an object of the present invention is to provide athree-port nonreciprocal circuit device that is connectable to abalanced output circuit without a balun, hybrid, or the like interposedtherebetween and that can reliably excite a ferrite even operated at alow operating point and to provide a composite electronic component anda communication apparatus including the circuit device.

To achieve the foregoing object, a three-port nonreciprocal circuitdevice according to the present invention includes:

(1) a permanent magnet;

(2) a ferrite to which a direct-current magnetic field is applied by thepermanent magnet; and

(3) a first center electrode, a second center electrode, and a thirdcenter electrode arranged so as to cross one another in an electricallyinsulated state.

(4) The circuit device is characterized in that at least one of thefirst to third center electrodes is constituted by a first lineconductor and a second line conductor which are arranged substantiallyparallel to each other, a hot end of the first line conductor and a coldend of the second line conductor oppose each other and a cold end of thefirst line conductor and a hot end of the second line conductor opposeeach other to cause electromagnetic coupling, and a port formed betweenthe hot end of the first line conductor and the hot end of the secondline conductor is a balanced port.

More specifically, preferably, each of the first and second lineconductors is constituted by at least two lines. Preferably, anelectrical length from the hot end of the first line conductor of thecenter electrode, constituted by the first line conductor and the secondline conductor, to the hot end of the second line conductor issubstantially one-half a wavelength.

The three-port nonreciprocal circuit device having the above-describedconfiguration can be connected to the output side of a balanced outputcircuit without a balanced-to-unbalanced converter, such as a balun,hybrid, or the like interposed therebetween.

Also, in order to achieve impedance matching between the three-portnonreciprocal circuit device and a balanced output circuit that isconnected thereto, for example, a matching capacitor is electricallyconnected in series with the hot end of first line conductor for thebalanced port and a matching capacitor is electrically connected inseries with the hot end of the second line conductor for the balancedport, a matching capacitor provides electrical connection between thehot end of the first line conductor and the hot end of the second lineconductor, or a matching capacitor provides electrical connectionbetween the hot end of the first line conductor and ground and amatching capacitor provides electrical connection between the hot end ofthe second line conductor and ground. Alternatively, the hot end of thefirst line conductor and the hot end of the second line conductor areelectrically connected to balanced input/output terminals via respectivematching capacitors, matching capacitors provide electrical connectionbetween the balanced input/output terminals, or matching capacitors areelectrically connected between the balanced input/output terminals andcorresponding grounds.

Varying the line width of the first line conductor and the second lineconductor of the center electrode for the balanced port from the linewidths of the other center electrodes can achieve optimum impedancematching between the nonreciprocal circuit device and the balancedoutput circuit. In particular, when the impedance of the balanced outputcircuit is low, increasing the line width of the first line conductorand the second line conductor relative to the line widths of the othercenter electrodes can reduce conduction loss and can provide anonreciprocal circuit device having low insertion loss.

A communication apparatus according to the present invention includesthe nonreciprocal circuit device having the above-described features andone pair of amplifiers that are driven at a phase difference ofsubstantially 180°. The balanced port of the three-port nonreciprocalcircuit device is connected to the balanced output terminals of the pairof amplifiers. With the above-described configuration, it is possible toprovide a compact communication apparatus having superior frequencycharacteristics.

According to the present invention, since the balanced input/outputterminals are provided, the three-port nonreciprocal circuit device canbe connected to a balanced circuit without a balanced-to-unbalancedconverter interposed therebetween. More specifically, the balanced inputterminals of the three-port nonreciprocal circuit device can beconnected to the balanced output terminals of the amplifiers that aredriven at a phase difference of substantially 180°. As a result, it ispossible to provide a compact communication apparatus having superiorfrequency characteristics. Further, since the cold ends of theinput-side center electrode are ground independently from each other,even when the amplifiers that drive the respective input ports areoperated at a low operating point (even when not all waves areamplified), the ferrite can be reliably excited.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of one embodiment of a three-portnonreciprocal circuit device according to the present invention.

FIG. 2 is an internal plan view of the three-port nonreciprocal circuitdevice shown in FIG. 1.

FIG. 3 is a schematic configuration view showing the internalconnections of the three-port nonreciprocal circuit device shown in FIG.1.

FIG. 4 is an electrical circuit diagram of a composite electroniccomponent in which the three-port nonreciprocal circuit device shown inFIG. 1 is electrically connected to a push-pull amplifier.

FIG. 5 is an electrical circuit diagram illustrating the operation ofthe composite electronic component shown in FIG. 4.

FIG. 6 is an electrical equivalent circuit diagram illustrating theoperation of the composite electronic component shown in FIG. 4.

FIG. 7 is an electrical equivalent circuit diagram illustrating theoperation of the composite electronic component shown in FIG. 4.

FIG. 8 is an electrical equivalent circuit diagram illustrating theoperation of the composite electronic component shown in FIG. 4.

FIG. 9 is an internal plan view showing a modification of the three-portnonreciprocal circuit device shown in FIG. 1.

FIG. 10 is an electrical equivalent circuit diagram of anotherembodiment of the composite electronic component according to thepresent invention.

FIG. 11 is an electrical equivalent circuit diagram of anotherembodiment of the three-port nonreciprocal circuit device according tothe present invention.

FIG. 12 is an electrical equivalent circuit diagram of still anotherembodiment of the three-port nonreciprocal circuit device according tothe present invention.

FIG. 13 is an electrical equivalent circuit diagram of still anotherembodiment of the three-port nonreciprocal circuit device according tothe present invention.

FIG. 14 is an electrical equivalent circuit diagram of yet anotherembodiment of the three-port nonreciprocal circuit device according tothe present invention.

FIG. 15 is an electrical equivalent circuit diagram of a furtherembodiment of the three-port nonreciprocal circuit device according tothe present invention.

FIG. 16 is an exploded perspective view of a still further embodiment ofthe three-port nonreciprocal circuit device according to the presentinvention.

FIG. 17 is an electrical circuit block diagram of one embodiment of acommunication apparatus according to the present invention.

FIG. 18 is an electrical equivalent circuit diagram showing anotherembodiment.

FIG. 19 is an electrical equivalent circuit diagram showing anotherembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of a three-port nonreciprocal circuit device, a compositeelectronic component, and a communication apparatus according to thepresent invention will be described below with reference to theaccompanying drawings. In each embodiment, an example of alumped-element isolator will be described as a three-port nonreciprocalcircuit device. The same components and the same portions are denotedwith the same reference numerals and redundant descriptions will not begiven.

First Embodiment, FIGS. 1 to 9

As shown in FIG. 1, an isolator 1 generally includes a lower metalcasing 4, a resin terminal casing 3, a center-electrode assembly 13, anupper metal casing 8, a permanent magnet 9, an insulating member 7, aresistor R, matching capacitors C1 to C3, and so on.

The center-electrode assembly 13 is configured such that centerelectrodes 21 to 23 are arranged, in an electrically insulated state, atthe upper surface of a circular-plate microwave ferrite 20 such that theangle of crossing one another is substantially 120°. The hot ends of thecenter electrodes 22 and 23 have connection portions 28 and 29,respectively, and the cold ends are connected to a ground electrode 25.

The center electrode 21 is constituted by a first line conductor 21 aand a second line conductor 21 b which are arranged parallel to eachother. The hot ends of the first line conductor 21 a and the second lineconductor 21 b have connection portions 27 and 26, respectively, and thecold ends are connected to the ground electrode 25. The first and secondline conductors 21 a and 21 b are arranged such that the hot end of thefirst line conductor 21 a and the cold end of the second line conductor21 b oppose each other and the cold end of the first line conductor 21 aand the hot end of the second line conductor 21 b oppose each other tocause electromagnetic coupling.

The line conductors 21 a and 21 b and the center electrodes 22 and 23are each constituted by two lines. In particular, constituting each ofthe line conductors 21 a and 21 b by two lines combines the effects ofexciting the ferrite 20, thereby allowing efficient excitation of theferrite. As a result, the insertion loss decreases and a high-efficienttransmission system can be achieved.

The ground electrode 25 common to the center electrode 21, 22, and 23 isprovided so as to substantially cover the lower surface of the ferrite20. The ground electrode 25, which is provided on the reverse surface ofthe ferrite 20, is connected to a button wall 4 b of the lower metalcasing 4 through a window portion 3 c of the resin terminal casing 3 bya method such as soldering or the like, thereby connecting thecenter-electrode assembly 13 to ground.

As shown in FIG. 2, balanced input terminals (=balanced inputterminals=differential input terminals) 14 and 15, an unbalanced outputterminal (=unbalanced output terminal) 16, and three ground terminals 17are insert-molded into the resin terminal casing 3. One end of each ofthe terminals 14 to 17 is extracted from opposing sidewalls 3 a of theresin terminal casing 3 toward the outside, and the other ends of theterminals 14 to 17 are exposed at a bottom portion 3 b of the resinterminal casing 3 to form balanced input extracting electrode portions14 a and 15 a, an unbalanced output extracting electrode portion 16 a,and ground extracting electrode portions 17 a, respectively. Thebalanced input extracting electrode portions 14 a and 15 a and theunbalanced output extracting electrode portion 16 a are soldered,respectively, to the connection portions 26, 27, and 28 of the centerelectrodes 21 and 22.

Each of the matching capacitor C1 to C3 is a single-plate capacitor inwhich a hot-side capacitor electrode and a cold-side capacitor electrodeare provided on the obverse and reverse surfaces of a dielectricsubstrate. The hot-side capacitor electrodes are soldered to thecorresponding connection portions 26 to 29 of the center electrodes 21to 23 and the cold-side capacitor electrodes are soldered to the groundextracting electrode portions 17 a, which are exposed at the resinterminal casing 3.

One end of the resistor R is connected to the hot-side capacitorelectrode of the matching capacitor C3 via the connection portion 29 ofthe center electrode 23, and the other end is connected to the groundextracting electrode portion 17 a exposed at the bottom portion 3 b ofthe resin terminal casing 3. That is, the matching capacitor C3 and theresistor R are electrically connected in parallel between the connectionportion 29 of the center electrode 23 and ground. FIG. 3 showselectrical connections inside the isolator 1.

The components having the above-described configuration are assembled,for example, as follows. As shown in FIG. 1, the lower metal casing 4 isattached to the resin terminal casing 3 from below. Next, thecenter-electrode assembly 13, the matching capacitors C1 to C3, theresistor R, and so on are accommodated in the resin terminal casing 3,and the upper metal casing 8 is attached. The permanent magnet 9 and theinsulating member 7 are arranged between the upper metal casing 8 andthe center-electrode assembly 13. The permanent magnet 9 applies adirect-current magnetic field H to the center-electrode assembly 13. Thelower casing 4 and the upper casing 8 are joined into a metal casing,which defines a magnetic circuit and also functions as a yoke.

FIG. 4 is an electrical circuit diagram of a composite electroniccomponent 40 in which the isolator 1 and a push-pull amplifier 31, whichoperates at a phase difference of 180°, are electrically connected.

Two opposite ends (specifically, the connection portions 26 and 27) ofthe center electrode 21 in the isolator 1 act as power-supply terminals,and an input port 1 is connected to the center electrode 21 and acts asa balanced input port. The balanced input port 1, which is connected tothe center electrode 21 in the isolator 1, is electrically connected toa balanced output side of the push-pull amplifier 31. An output port 2is connected to the center electrode 22 in the isolator 1 and acts as anunbalanced output port. A port 3 is connected to the center electrode 23in the isolator 1 and acts as a termination port.

On the other hand, the push-pull amplifier 31 has a structure in whichone pair of amplifier devices, i.e., transistors Tr1 a and Tr1 b, andone pair of amplifier devices, i.e., transistors Tr2 a and Tr2 b, areconnected at two stages. For example, bipolar transistors, as well asfield-effect transistors in this first embodiment, may be used as thetransistors Tr1 a to Tr2 b.

The initial-stage transistors Tr1 a and Tr1 b are electrically connectedto the final-stage transistors Tr2 a and Tr2 b via an interstagematching circuit 52. Bias circuits, which include resistors R12 andcapacitors C13, are electrically connected to the sources of theinitial-stage transistors Tr1 a and Tr1 b. The sources of thefinal-stage transistors Tr2 a and Tr2 b are electrically connected toground.

The interstage matching circuit 52 includes inductors L14, capacitorsC15, inductors L13, a capacitor C14, inductors L15, and a capacitor C16.The inductors L14 and the capacitors C15 are electrically connected inseries between the drains of the initial-stage transistors Tr1 a and Tr1b and the corresponding gates of the final-stage transistors Tr2 a andTr2 b. The inductors L13 and the capacitor C14 are electricallyconnected between the drains of the initial-stage transistors Tr1 a andTr1 b and a drain power-supply terminal 43 of the initial-stagetransistors Tr1 a and Tr1 b. The inductors L15 and the capacitor C16 areelectrically connected between the gates of the final-stage transistorsTr2 a and Tr2 b and a gate bias power-supply terminal 44 of thefinal-stage transistors Tr2 a and Tr2 b.

The initial-stage transistors Tr1 a and Tr1 b are electrically connectedto balanced input terminals 41 a and 41 b via an input matching circuit51. The input matching circuit 51 includes inductors L12 and resistorsR11. The inductors L12 are electrically connected in series between thegates of the initial-stage transistors Tr1 a and Tr1 b and thecorresponding input terminals 41 a and 41 b, and the resistors R11 areelectrically connected between the input terminals 41 a and 41 b andground.

The final-stage transistors Tr2 a and Tr2 b are electrically connectedto the balanced output terminals 14 and 15 of the push-pull amplifier 31(in other words, to the balanced input terminals of the isolator 1) viaan output matching circuit 53. The output matching circuit 53 includesinductors L17, capacitors C18, inductors L16, and capacitors C17. Theinductors L17 and the capacitors C18 are electrically connected inseries between the drains of the final-stage transistors Tr2 a and Tr2 band the corresponding balanced output terminals 14 and 15 of thepush-pull amplifier 31. The inductors L16 and the capacitors C17 areelectrically connected between the drains of the final-stage transistorsTr2 a and Tr2 b and a drain power-supply terminal 48 of the final-stagetransistors Tr2 a and Tr2 b.

Next, the operation of the composite electronic component 40 having theabove-described configuration will be described with reference toequivalent circuit diagrams shown in FIGS. 5 to 8.

FIG. 5 shows a state in which the setting is such that some amount ofidling current in the absence of an input signal (i.e., some amount ofbias current during a no signal period) flows. That is, both of thetransistors Tr2 a and Tr2 b are in ON states. With this setting,significantly low output-signal distortion can be expected. In FIG. 5,reference characters RL1 indicate input load resistors and referencecharacter RL2 indicates an output load resistor.

FIG. 6 shows a state in which balanced signal having a phase differenceof 180° are input between the balanced input terminals 41 a and 41 b andthe phase difference of the balanced signals is θ°. When the balancedsignals are input to the terminating transistors Tr2 a and Tr2 b,respectively, the transistor Tr2 a is put into the ON state and thetransistor Tr2 b is put into the OFF state. Current flowing through thetransistor Tr2 a flows through the first line conductor 21 a of thecenter electrode 21, to thereby cause the ferrite 20 to generate ahigh-frequency magnetic field. At this point, the second line conductor21 b is open since the transistor Tr2 b is in the OFF state and the coldend of the first line conductor 21 a is connected to ground. Thus,regardless of the state of the second line conductor 21 b, the ferrite20 constantly generates a high-frequency magnetic field. Thishigh-frequency magnetic field causes current to flow through the centerelectrode 22, which is electromagnetically coupled with the first lineconductor 21 a. As a result, the balanced signals are transmitted fromthe balanced input terminals 41 a and 41 b to an unbalanced outputterminal 16.

FIG. 7 shows a state in which the phases of the balanced signals areθ+180°. When the balanced signals are input to the terminatingtransistors Tr2 a and Tr2 b, respectively, the transistor Tr2 a is putinto the OFF state and the transistor Tr2 b is put into the ON state.Thus, current flowing through the transistor Tr2 b flows through thesecond line conductor 21 b of the center electrode 21, to thereby causethe ferrite 20 to generate a high-frequency magnetic field. Thishigh-frequency magnetic field causes current to flow through the centerelectrode 22, which is electromagnetically coupled with the second lineconductor 21 b. Consequently, the balanced signals are transmitted fromthe balanced input terminals 41 a and 41 b to the unbalanced outputterminal 16.

As described, the cold ends of the first and second line conductors 21 aand 21 b of the input-side center electrode 21 are connected to groundindependently from each other. Thus, even when the push-pull amplifier31 connected to the balanced input port 1 is operated at a low operatingpoint equivalent to class B or lower (i.e., even when not all waves areamplified), the ferrite 20 can reliably generate a high-frequencymagnetic field.

Conversely, when an unbalanced signal is input to the unbalanced outputterminal 16, current flows through the center electrode 22 and theferrite 20 generates a high-frequency magnetic field. Thishigh-frequency signal causes current to flow through the centerelectrode 23, which is magnetically coupled with the center electrode22. The current that flowed through the center electrode 23 flowsthrough the terminating resistor R, where the majority of power isconsumed and the resulting electricity flows to ground. Thus, almost nounbalanced signal is transmitted from the unbalanced output terminal 16to the balanced output terminals 41 a and 41 b.

FIG. 8 shows a state in which the setting is such that almost no idlingcurrent in the absence of an input signal (i.e., almost no bias currentduring a no-signal period) flows. That is, both of the transistors Tr2 aand Tr2 b are in the OFF states. In this setting, while the efficiencyis slightly increased, the output signal distortion is slightlyincreased.

This isolator 1 can be connected to the output side of the push-pullamplifier 31 (an unbalanced output circuit) without abalanced-to-unbalanced converter, such as a balun or hybrid, interposedtherebetween. This can reduce the size and cost of the compositeelectronic component 40. Further, since a balun, hybrid, or the like canbe omitted, it is possible to provide a composite electronic component40 having low insertion loss, low unwanted radiation, and a largeavailable frequency band.

Also, adjusting the electrostatic capacity value of the matchingcapacitors C1, which provide electrical connections between theconnection portions 26 and 27 located at two opposite ends of the centerelectrode 21 for the balanced input ports 1 and corresponding grounds,can adjust the operating center frequency of a transmission circuitsection to an intended frequency. Further, since two-opposite ends ofthe center electrodes 21 are not electrically connected via a capacitorin this configuration, unwanted parasitic inductance componentsassociated with lead lines and so on does not generate.

It is preferable that the electrical length of the center electrodes 21to 23 is set to be one-half the wavelength. When the electrical lengthof the center electrode 21 for the balanced port 1, in other words, theelectrical length from the hot ends to the cold ends of the first andsecond line conductors 21 a and 21 b, is set to one-half the wavelength,the impedance between the connection portions 26 and 27 at two oppositeends of the center electrode 21 becomes infinite and the reactanceinterposed between the balanced transmission lines becomes infinite.That is, there is no need to connect a matching capacitor to the centerelectrode 21. When the reactance interposed between the balancedtransmission lines is close to infinite, the degree of impedanceconversion performed by the matching capacitor is reduced and theoperating band of the isolator is also increased.

In addition, setting the line width of the first and second lineconductors 21 a and 21 b of the center electrode 21 to be different fromthe electrode width of the other center electrodes 22 and 23 can achieveoptimum impedance matching with the push-pull amplifier 31.

In particular, when the push-pull amplifier 31 is operated with powersupply with a relatively low-voltage power supply, the impedance of thepush-pull amplifier 31 is reduced, so that a large current flows throughthe center electrode 21. In this case, as an isolator 1 a shown in FIG.9, the line width of the line conductors 21 a and 21 b of the centerelectrode 21 for the balanced input port 1 is increased relative to theline width of the other center electrodes 22 and 23. This reduces theequivalent series resistance of the center electrode 21 and reduces theconductor loss of the center electrode 21, thereby making it possible toprovide an isolator 1 a having low insertion loss.

Also, when the push-pull amplifier 31 has the balanced input terminals41 a and 41 b as in the first embodiment, connection with a SAW filter,a balanced buffer amplifier, an AGC amplifier, or a Gilbert-celldouble-balanced mixer is facilitated. Further, since an unwanted signalinput at the same phase is not amplified, this arrangement makes itdifficult for an unwanted signal to be amplified. Thus, it is possibleto eliminate provisions, such as a circuit required for removingunwanted waves.

Second Embodiment, FIG. 10

FIG. 10 is an electrical circuit diagram of a composite electroniccomponent 40A according to a second embodiment. In FIG. 10, referencenumeral 51 indicates a hybrid coupler that is an unbalanced-to-balancedconverter circuit and that has distributed-constant lines (strip lines)52 to 55, and reference numeral R15 indicates a terminating resistor.

Two opposite ends (specifically, the connection portions 26 and 27) ofthe center electrode 21 in the isolator 1 act as power-supply terminals,and the input port 1, which is connected to the center electrode 21 inthe isolator 1, acts as a balanced input port. The balanced input port1, which is connected to the center electrode 21 in the isolator 1, iselectrically connected to a balanced output side of the push-pullamplifier 31. A phase shifter 56 is connected in series with onebalanced input end of the push-pull amplifier.

The composite electronic component 40A having the above-describedconfiguration provides the same advantages as the composite electroniccomponent 40 of the first embodiment. As in the second embodiment, whenthe input side of the push-pull amplifier 31 is an unbalanced type,connection with a dielectric filter, LC filter, helical filter,unbalanced buffer amplifier, or AGC amplifier can be facilitated. Also,since only one input terminal is required, a wiring and packaging areacan be reduced and the configuration can be simplified.

The unbalanced-to-balanced converter circuit may be implemented with apassive circuit, including a power splitter, delay line, or balun, ormay be implemented with active devices, such as bipolar transistors orfield-effect transistors. In addition, it is preferable that theunbalanced-to-balanced converter circuit be integrated into a multilayersubstrate. The unbalanced-to-balanced converter circuit integrated intothe multilayer substrate is convenient since the operation thereof isstable and the matching capacitors C1 to C3 of the isolator 1 can alsobe integrated into the multilayer substrate.

Third to Seventh Embodiment, FIGS. 11 to 15

FIG. 11 is an electrical equivalent circuit diagram of an isolator 61according to a third embodiment. In this isolator 61, the hot ends ofthe first and second line conductors 21 a and 21 b of the centerelectrode 21 act as power-supply terminals and a port 1 connected tothose hot ends act as a balanced input port. A matching capacitor C4 iselectrically connected between the hot end of the first line conductor21 a and the hot end of the second line conductor and matchingcapacitors C5 are electrically connected in series with the hot ends ofthe first and second line conductors 21 a and 21 b. Appropriatelyadjusting the electrostatic capacitance values of the matchingcapacitors C4 and C5 allows the operating center frequency of anelectrical circuit (e.g., the transmission circuit section of a portabletelephone) including the isolator 61 to be adjusted to an intendedfrequency. Additionally, it is possible to achieve impedance matchingwith a balanced output circuit having an output impedance greatly awayfrom 50 Ω.

FIG. 12 is an electrical equivalent circuit diagram of an isolator 71according to a forth embodiment. In this isolator 71, matchingcapacitors C4 are electrically connected between the hot ends of firstand second line conductors 21 a and 21 b of the center electrode 21 andcorresponding grounds, and matching capacitors C5 are electricallyconnected in series with the hot ends of the first and second lineconductors 21 a and 21 b, respectively. Appropriately adjusting theelectrostatic capacitance values of the matching capacitors C4 and C5allows the operating center frequency of a transmission circuit sectionto be adjusted to an intended frequency. Additionally, it is possible toachieve impedance matching with a balanced output circuit having anoutput impedance greatly away from 50 Ω.

FIG. 13 is an electrical equivalent circuit diagram of an isolator 81according to a fifth embodiment. In this isolator 81, matchingcapacitors C5 are electrically connected between the hot ends of thefirst and second line conductors 21 a and 21 b of the center electrode21 and the corresponding balanced input terminals 14 and 15.Appropriately adjusting the electrostatic capacitance values of thematching capacitors C5 can achieve impedance matching with a balancedoutput circuit having a low output impedance (e.g., 10 Ω or less).

FIG. 14 is an electrical equivalent circuit diagram of an isolator 91according to a sixth embodiment. In this isolator 91, matchingcapacitors C5 are electrically connected between the hot ends of thefirst and second line conductors 21 a and 21 b of the center electrode21 and the corresponding balanced input terminals 14 and 15, and amatching capacitor C4 is electrically connected between the balancedinput terminals 14 and 15. Appropriately adjusting the electrostaticcapacitance values of the matching capacitors C4 and C5 allows theoperating center frequency of a transmission circuit section to beadjusted to an intended frequency. Additionally, it is possible toachieve impedance matching with a balanced output circuit having anoutput impedance greatly away from 50 Ω.

FIG. 15 is an electrical equivalent circuit diagram of an isolator 101according to a seventh embodiment. This isolator 101 has a configurationin which matching capacitors C4 are connected between the balanced inputterminals 14 and 15 and corresponding grounds in the isolator 81 of thesixth embodiment shown in FIG. 13.

Eighth Embodiment, FIG. 16

As shown in FIG. 16, a three-port isolator 171 generally includes ametal casing defined by a lower metal casing 174 and an upper metalcasing 178, a permanent magnet 179, a center electrode assembly 190, arectangular multilayer substrate 200 that includes a terminatingresistor R and matching capacitors C1 to C3.

In the center electrode assembly 190, center electrodes 191, 192, and193 are arranged on the upper surface of a microwave ferrite 194, whichhas a rectangular shape in plan view, so as to cross one another bysubstantially 120° with an insulating layer (not shown) therebetween. Inthe eighth embodiment, each of the center electrodes 192 and 193 isconstituted by two lines.

The center electrode 191 is constituted by a first line conductor 191 aand a second line conductor 191 b which are arranged parallel to eachother. The first and second line conductors 191 a and 191 b are arrangedsuch that the hot end of the first line conductor 191 a and the cold endof the second line conductor 191 b oppose each other and the cold end ofthe first line conductor 191 a and the hot end of the second lineconductor 191 b oppose each other to cause electromagnetic coupling.

The center electrodes 191 to 193 may be attached to the ferrite 194 byusing copper films or may be formed by printing a conductive pastecontaining Ag, Au, Ag—Pd, or Cu on the ferrite 194. The conductive pastecontains a photosensitive resin. After the conductive paste is printedon the entire surface of the ferrite 194, the ferrite 194 is exposed tolight and is subjected to development processing, unwanted portions areremoved, and the resulting structure is fired. As a result, thethick-film center electrodes 191 to 193 having high positional accuracyare formed, and thus stable electrical characteristics are provided.

The multilayer substrate 200 includes a dielectric sheet havingcenter-electrode hot-end connection terminals 182 a, 182 b, 183, and184, center-electrode cold-end connection terminals 185, and so on; adielectric sheet having capacitor electrodes, a resistor R, and so on onthe surface; balanced input terminals 214 and 215; an unbalanced outputterminal 216; ground terminals 217; and so on.

This multilayer substrate 200 is fabricated as follows. That is, thedielectric sheets are made of dielectric material that sinters at a lowtemperature. The dielectric material contains Al₂O₃ as the maincomponent and contains one or more types of SiO₂, SrO, CaO, PbO, Na₂O,K₂O, MgO, BaO, CeO₂, and B₂O₃ as a sub-component.

In addition, shrink-restraining sheets, which do not sinter under thefiring conditions (especially, at a firing temperature of 1000° C. orless) of the multilayer substrate 200, are formed to restrain firingshrinkage of the multilayer substrate 200 in the substrate planedirection (the X-Y direction) thereof. Material for theshrink-restraining sheets is a mixed material of alumina powder andstabilized zirconia powder.

The center-electrode connection electrodes 182 a to 185 and thecapacitor electrodes are formed on the dielectric sheets by a methodsuch as screen printing or photolithography. For example, Ag, Cu, orAg—Pd that has low resistivity and that can be fired concurrently withthe dielectric sheets is used as material for the electrodes 182 a to185 and so on.

The resistor R is formed on a surface of the dielectric sheet by amethod, such as screen printing. Cermet, carbon, ruthenium, or the likeis used as material for the resistor R.

Signal via-holes are formed by pre-forming holes for via holes in thedielectric sheets by laser processing, punching, or the like, and thenfilling the holes with a conductive paste. Typically, as material forthe conductive paste, material (Ag, Cu, Ag—Pd, or the like) that is thesame as that for the electrodes 182 a to 185 and so on is used.

The capacitor electrodes oppose each other with a correspondingdielectric sheet interposed therebetween to constitute the matchingcapacitors C1 to C3. These matching capacitors C1 to C3 and theterminating resistor R, together with the electrodes 182 a to 185 andthe signal via-holes, constitute an electrical circuit, which is similarto the isolator 1 shown in FIG. 4, within the multilayer substrate 200.

The dielectric sheets described above are stacked, theshrink-restraining sheets are further stacked on the upper and lowersides of the stack, and then the resulting structure is fired. As aresult, a laminate is provided. Thereafter, unsinteredshrink-restraining material is removed by supersonic cleaning or wethoning to thereby provide the multilayer substrate 200.

The balanced input terminals 214 and 215, the unbalanced output terminal216, and the ground terminal 217 are arranged at the bottom surface ofthe multilayer substrate 200 so as to protrude therefrom. Ni plating of1 to 10 μm is provided on surfaces of the thick-film terminals 214 to217 and gold plating of 0.5 μm or less is further provided on thosesurfaces. The plating is intended to improve the solderability (solderwettability) of the terminals 214 to 217, prevent melting to solder(solder leading), and prevent migration.

The components described above are fabricated as follows. That is, thepermanent magnet 179 is secured to the ceiling of the upper metal casing178 with an adhesive. Ends of the center electrodes 191 to 193 of thecenter-electrode assembly 190 are soldered to the center-electrodeconnection electrodes 182 a to 185 formed at the surface of themultilayer substrate 200, thereby mounting the center-electrode assembly190 on the multilayer substrate 190.

The multilayer substrate 200 is placed on a bottom portion 174 b of thelower metal casing 174, and a ground electrode provided at the reversesurface of the multilayer substrate 200 is fixed and electricallyconnected to the bottom portion 174 b by soldering.

Since the center electrodes 191 to 193 and the multilayer substrate 200in the isolator 171 are formed by screen printing or photolithography, acomplicated circuit and wiring can be formed with high accuracy.

In the present embodiment, the first line conductor 191 a and the secondline conductor 191 b of the center electrode 191 for the balanced inputport are arranged adjacent to each other. Thus, there is a need toensure that short-circuiting does not occur even with the adjacentarrangement and a characteristic variation due to a spacing variationbetween individual products does not occur. It is therefore effective touse the printing or photolithography technique to form the centerelectrodes 191 to 193 with high accuracy.

In generally, photolithography can form patterns with higher accuracythan printing. However, since a thin film suitable for photolithographyhas a small electrode thickness, the amount of loss is large in afrequency band of about 1 to 2 GHz. Accordingly, the method in whichfiring is performed after removing unwanted portions of unfiredthick-film electrodes by a photolithography-based exposure/developmenttechnique is the most suitable for the formation of the centerelectrodes 191 to 193 in the isolator 171 of the eighth embodiment.

In the present embodiment, since the number of matching capacitors C1 toC3 is greater than the number in a typical isolator, the use of matchingcapacitors in the form of separate components increases the numbercomponents and the number of connection portions to thereby reduce thereliability, which is disadvantageous for miniaturization. However,integrating the push-pull amplifier 31 or some inductors and/orcapacitors of the unbalanced-to-balanced converter or the like,connected to the input side of the push-pull amplifier 31, into themultilayer substrate 200 can provide a miniaturized, highly-reliablecomposite electronic component.

Ninth Embodiment, FIG. 17

In a ninth embodiment, a communication apparatus according to thepresent invention will be described in the context of a portabletelephone by way of example.

FIG. 17 is an electrical circuit block diagram of an RF section of aportable telephone 220. In FIG. 17, reference numeral 222 indicates anantenna device, 223 is a duplexer, 231 is a sending-side isolator, 232is a sending-side power amplifier, 233 is a sending-side interstagebandpass filter, 234 is a sending-side mixer, 235 is a receiving-sidepower amplifier, 236 is a receiving-side interstage bandpass filter, 237is a receiving-side mixer, 238 is a voltage controlled oscillator (VCO),and 239 is a local bandpass filter.

In this case, the composite electronic component 40 of the firstembodiment or the composite electronic component 40 a of the secondembodiment is used as a composite electronic component 240.Incorporating the composite electronic component 240 can achieve ahighly-reliable, compact, portable telephone 20 having improvedelectrical characteristics.

Other Embodiments

The present invention is not limited to the above-described embodiments,and thus various changes can be made thereto within the scope of thesubstance of the present invention. For example, the three-portnonreciprocal circuit device according to the present invention may be athree-port nonreciprocal circuit device included in a circulator or acoupler, other than an isolator.

Also, the center electrodes other than the center electrode for thebalanced input port may be connected to balanced ports or may beconnected to unbalanced ports. In this case, as in a three-pointisolator 61A shown in FIG. 18, two opposite ends of the centerelectrodes 22 and 23, connected to balanced ports 2 and 3, may beconfigured as hot ends and the centers of the center electrodes 22 and23 may be configured as virtual ground points (cold ends).Alternatively, as in a three-port isolator 61B shown in FIG. 19, acenter electrode 22 connected to a balanced output port 2 may beconstituted by a first line conductor 22 a and a second line conductor22 b which are arranged substantially parallel to each other. Further,the arrangement may be such that the hot end of the first line conductor22 a and the cold end of the second line conductor 22 b oppose eachother and the cold end of the first line conductor 22 a and the hot endof the second line conductor 22 b oppose each other for electromagneticcoupling.

INDUSTRIAL APPLICABILITY

As described above, the present invention is effectively applicable tothree-port nonreciprocal circuit devices, such as isolators, used in amicrowave band; to composite electronic components for transmissioncircuits and so on including the nonreciprocal circuit devices; and tocommunication apparatuses, such as portable telephones. In particular,the present invention is superior in that the circuit device can beconnected to a balanced output circuit without a balun, hybrid, or thelike interposed therebetween and the ferrite is reliably excited evenwhen operated at a low operating point.

1. A three-port nonreciprocal circuit device comprising: a permanent magnet; a ferrite to which a direct-current magnetic field is applied by the permanent magnet; and a first center electrode, a second center electrode, and a third center electrode arranged so as to cross one another in an electrically insulated state; and at least one of the first to third center electrodes comprising a first line conductor and a second line conductor arranged substantially parallel to each other such that a hot end of the first line conductor and a cold end of the second line conductor oppose each other and a cold end of the first line conductor and a hot end of the second line conductor oppose each other to cause electromagnetic coupling, wherein a port formed between the hot end of the first line conductor and the hot end of the second line conductor is a balanced port.
 2. A communication apparatus, comprising at least one nonreciprocal circuit device according to claim
 1. 3. The three-port nonreciprocal circuit device according to claim 1, wherein the electrical length from the hot end of the first line conductor to the hot end of the second line conductor of the first center electrode is substantially one-half a wavelength.
 4. The three-port nonreciprocal circuit device according to claim 1, having a matching capacitor in an electrical connection between at least one of (a) the hot end of the first line conductor and the hot end of the second line conductor and (b) the hot end of the first line conductor and a ground and the hot end of the second line conductor and a ground.
 5. The three-port nonreciprocal circuit device according to claim 1, having a first matching capacitor electrically connected in series with the hot end of the first line conductor and a second matching capacitor electrically connected in series with the hot end of the second line conductor.
 6. A composite electronic component comprising an output circuit electrically connected to a three-port nonreciprocal circuit device according to claim
 1. 7. The three-port nonreciprocal circuit device according to claim 1, wherein the first and at least one other center electrode comprises first and second line conductors, and the width of each line of the first line conductor and the second line conductor of the first center electrode is different from the widths of lines of the other center electrodes.
 8. The three-port nonreciprocal circuit device according to claim 7, wherein the width of each line of the first line conductor and the second line conductor of the first center electrode is greater the widths of the lines of the other center electrodes.
 9. The three-port nonreciprocal circuit device according to claim 1, wherein that each of the first line conductor and the second line conductor is constituted by at least two lines.
 10. The three-port nonreciprocal circuit device according to claim 9, wherein the first and at least one other center electrode comprises first and second line conductors, and the width of each line of the first line conductor and the second line conductor of the first center electrode is different from the widths of lines of the other center electrodes.
 11. The three-port nonreciprocal circuit device according to claim 10, wherein the width of each line of the first line conductor and the second line conductor of the first center electrode is greater the widths of the lines of the other center electrodes.
 12. The three-port nonreciprocal circuit device according to claim 11 wherein the electrical length from the hot end of the first line conductor to the hot end of the second line conductor of the first center electrode is substantially one-half a wavelength.
 13. The three-port nonreciprocal circuit device according to claim 12, having a matching capacitor in an electrical connection between the hot end of the first line conductor and the hot end of the second line conductor.
 14. The three-port nonreciprocal circuit device according to claim 12, having a first matching capacitor in an electrical connection between the hot end of the first line conductor and a ground and a second matching capacitor in an electrical connection between the hot end of the second line conductor and a ground.
 15. The three-port nonreciprocal circuit device according to claim 12, having a first matching capacitor electrically connected in series with the hot end of the first line conductor and a second matching capacitor electrically connected in series with the hot end of the second line conductor.
 16. The three-port nonreciprocal circuit device according to claim 14, having the hot end of the first line conductor and the hot end of the second line conductor electrically connected to balanced input/output terminals via respective matching capacitors and matching capacitors electrically connected between the balanced input/output terminals and corresponding grounds.
 17. A composite electronic component comprising: an amplifier driven at a phase difference of substantially 180° and having balanced output terminals; and the nonreciprocal circuit device according to claim 1, the balanced port being connected to balanced output terminals of the amplifier.
 18. A communication apparatus, comprising at least one composite electronic component according to claim
 17. 19. A composite electronic component according to claim 17, wherein the amplifier has balanced input terminals.
 20. The composite electronic component according to claim 19, wherein unbalanced input terminals are connected to balanced input terminals of the amplifier via an unbalanced-to-balanced converter circuit. 